When we received the full structural engineering design for the Living House we were mildly HORRIFIED at the amount of reinforcing and concrete that our supposedly uber sustainable house required.
We could not reconcile all of this with the fact that we are trying to have a light footprint on the planet and we are wondering if we have made a big mistake. However to be a little bit fair to us we are on a constrained site and therefore need to go 2 storeys to accommodate the ETS beds. And to be even more honest we are in love with the look and feel of rammed earth and prefer it massively to the other types of earthen construction. But we are still horrified. We did have one brilliant idea for eliminating some concrete, Going back to the original idea for an earthen floor on the ground floor of the house (with the exception of the garage).
What we have found is that the choice of materials for a project is a massively complex issue that needs careful consideration. In all of my experience in construction and sustainability I have yet to find a way to definitively compare the selection of different materials over the entire lifecycle of a house to determine what is the most sustainable choice. A lot of LCA tools will look at what they call the life cycle analysis of a project, however I have yet to find one that takes into account things like durability, maintenance and resilience. For example if we build out of rammed earth, that requires increased reinforcing and concrete, we will create a house that requires no exterior maintenance. If we had constructed the Living House out of cedar timber weatherboards of even lightweight straw bale, we would have created a house that would require yearly maintenance in terms of painting and/or re-plastering. It is not clear to me how this ongoing maintenance load is accounted for in many LCA tools and where the materials and labour (mileage etc) is added into the mix. In addition rammed earth houses can stand for hundreds of years without requiring any maintenance. Can the same be said for a timber house that is built to last only 50 years? Where is that taken into account in the LCA tools. Therefore have we created a more sustainable house or not? We need more upfront materials like concrete and reinforcing, however we will require nothing else ever again. In the long term what is better?
One argument for timber is that it is carbon neutral so having to replace it ever 50 years or so is ok. But does that account for the oil that is required for felling, trucking, milling, transport to site etc. As well as the paint or stains/sealants.
All I know is that it is a really complex issue and I don’t think that there is yet any definitive way to compare different options (but if someone knows of one do let me know as I am very interested!)
However what I do know is that the companies that work in the space of the concrete and cement industry are working very hard to lessen their footprint on the planet. Even though I work full time in the sustainability industry I was surprised to find out all of the initiatives that Firth and Golden Bay Cement have in place to make their products as sustainable as possible.
The cement that is used in Firth’s concrete is from Golden Bay Cement (GBC) and is Declare labelled as red list free. GBC cement is NZ manufactured ,not imported as all other cement in NZ is. GBC use 30% alternative fuels from the timber industry which would have ended up in landfill, recently receiving a grant to gear up to divert some 3 million used tyres from landfill, providing a further increase in alternative fuel use – some 15% . The advanced GBC cement plant operates at such high temps that this is an environmentally friendly disposal option for tyres.
GBC are due to release their LCA findings in the form of an EPD this month – the carbon emission results are far better than the default values currently used in building LCA models, which are based onoverseas data.
Golden Bay Cement tyre fuel funding article: http://www.fletcherbuilding.com/who-we-are/news/fletcher-building-and-government-partner-to-invest-in-sustainability-at-golden-bay-cements-portland-plant/
Golden Bay Cement Declare Label: https://access.living-future.org/golden-bay-cement-eversure%E2%84%A2-gp-and-everfast%E2%84%A2-he-cement
As for Firth, Most of the 80 plants nationally recycle water and the wet concrete that is returned in trucks is recycled – either into moulds to provide barriers in Landscape yards or some of the larger plants have recycle machines to separate the aggregates and sands from the slurry to reuse in the next batch of concrete.
Firth manufacture from locally sourced raw materials to minimise cartage movement, GPS and monitor their trucks to maximise energy, fuel and time efficiency. To further look after their resources they widely educate the market on design and use of masonry and concrete for durability and longevity, Thermal gain, Fire ratings and recycling – cradle to grave + reuse.”
I originally asked if perhaps we could consider replacing the cement with Flyash. However Huntly power station is not burning any longer so NZ does not have its own supply of fly ash any longer. When Huntly was operational concrete was a good place for the flyash rather than in landfill. However currently now Flyash is imported from India/China and further afield which does not make sense for environmental purposes – as well as quality of that fly ash being somewhat questionable sometimes.
So in summary this is a really complex issue and I don’t think that there is yet any definitive way to compare different house construction material options yet (but again if someone knows of one do let me know as I am very interested!)